1. Field of the Invention
The present invention relates to fluidized particle production systems and processes for producing fluidized particles and is useful in particular, but not exclusively, for the production of fluidized ice particles for ice blasting.
2. Description of the Related Art
Several systems have been devised to carry out one or more functions of ice formation and removal, and ice particle formation and transport. The removal or harvesting of ice from ice forming surfaces of ice making units has been carried out by various methods, including melting, the use of gravity, scrapers, or other mechanical means and a combination of the above, some of which are described in U.S. Pat. Nos. 2,344,922; 2,995,017; 4,389,820; 4,707,951 and 4,965,968. Ice particle formation has been carried out by scraping or harvesting (U.S. Pat. No. 2,344,922) or other methods involving grinding or crushing. Induction, gravity and mechanical feed technologies have been used to facilitate ice particle transport in U.S. Pat. Nos. 4,707,951; 4,389,820; 2995,017; 2,344,922; 4,965,968 and 2,724,949.
Batch atmospheric or "pressure pot" systems are known and used for relatively non-degradable media wherein a pre-manufactured medium is loaded in batches into a holding vessel for subsequent treatment such as sizing of particles, agitation and dispensing for transport. Such systems may be simplified and improved in terms of capital and operational costs and complexity by continuous or semi-continuous systems.
There are inherent problems in existing partially sealed continuous systems, especially those used for particle transport and blast treatment. These systems use a purge medium of air or other gas, e.g. carbon dioxide, in order to prevent humidity and heat intrusion, and to minimize icing, agglomeration and fluidization difficulties. It is also desirable to be able to quickly stop and start the systems between continuous running.
Such purging, with the associated capital, production and operational costs, is one of the most costly items in the system. Without total effective sealing, its practical use is wasteful. Costs may be reduced by minimizing the volume required, and by maximizing its usage.
Prior art systems attempt to isolate particle production from treatment which comprises conditioning, including sizing, cooling and drying, and also from transport of the particles. This requires costly and complicated equipment and delicate balance of control between process unit operations.
The present invention may be most immediately employed in systems which use nozzles employing inductive suction for transport and/or blast effect. In such systems, purge medium flow for effecting fluidized transport of the particles is one of the most important factors in an inductive type nozzle for transport and blast treatment effect. Therefore, the control and amount of the purge medium is not only necessary for correct efficient particle making, treatment and transport, but also for correct operation of the inductive nozzle for transport and the operation of a final nozzle for blast effect.
Prior art continuous systems comparable to the present invention are usually operated under partially or wholly unsealed ambient pressure conditions and as a result suffer from inefficiency and high equipment and skilled operator labour costs, which, are caused by agglomeration and plugging arising from humidity intrusion and system pressure imbalance, which requires delicate adjustment to correct system pressure and flow imbalance. In practice, high power and labour intensive mechanical equipment such as sealing arrangements, airlocks, vibrators, pumps and alpha radiation have been used in an attempt to correct these deficiencies but, as with efforts to seal part of the system in order to increase system efficiency, have only created further complexity and cost. Consequently, there is a need for a simplified system that can reduce mechanical, capital and operational costs while preserving the integrity of the solids by means of integrating isolated particle production, sizing and fluidizing.
Prior art systems employing positive pressure have been limited to partially sealed or individually sealed sub-systems or batch operation, agitation, prevention of clogging or short distance fluidization as typified in U.S. Pat. Nos. 4,048,757 and 5,071,289.